This invention generally relates to a method and apparatus for reducing the temperature of bakery products immediately after the discharge thereof from the baking oven.
A particularly interesting form of bakery products in this connection is bread. The last stage of the baking process of a loaf of bread takes place in an oven having a temperature of from 200.degree. to 270.degree. C. with a baking time which varies from 45 minutes to 20 minutes, depending upon the temperature and the cross-section of the loaf of bread. The crumb of the loaf has a temperature of about 95.degree. C. at the termination of the baking time, whereas the temperature of the crust is about 150.degree. C., the former temperature having been rather constant during the last part of the baking time because of evaporation of the moisture content in the loaf of bread.
For a number of different reasons it has been common practice to wrap bakery products, in particular bread, in bags for distribution and sale.
If the loaves are packed directly from the oven, the bag cannot be closed since the vapour from the interior of the loaf cannot find any path of escape and condenses on the inner side of the bag. This makes the bag soft. If a bag of plastic material is used, the surface of the loaf of bread will be softened by the water resulting from the condensed vapour. In the case of bread for which a crisp crust is a quality criterion (wheat bread), care should be taken during packing of the warm loaves that the open bag with its content is put in an upright position so that easy vapour escape is secured. The use of plastic materials for packing bread types having a long shelf life or good keeping qualities (whole meal bread) is not possible unless the loaves are first cooled. Bakers who have found it advantageous to sell whole meal bread in closed bags of plastic material therefore must provide for the cooling of the loaves of bread at least for one hour before packing, either by loading them on shelf carriages which are rolled into large cooling halls, or by means of a conveyor system which takes the loaves on a round trip lasting an hour or so. Such arrangements are very labour-consuming and/or require large investments.
Cooling of the loaves of bread in the above arrangement takes place as a combination of (a) radiation, (b) convection and (c) evaporation. If a high relative humidity is maintained in the cooling space, the evaporation rate will be lower, which means that the loss of bread weight is reduced, which of course, is of importance. The reduced loss, however, must be seen in relation to the expenses in the form of labour, time and capital which are necessary in order to obtain this result.
It is known that cooling of bakery products can be effected by means of vacuum treatment, which is described in "The Bakers Digest", Oct. 1949 and in "The Arkady Review", Volume 49, No. 2, 1973. The previously described methods for the vacuum cooling of bread, however, have not been completely successful and in particular have not made it possible to obtain a maximum of processing capacity with reasonable installation and operation expenses for the necessary equipment. An important requirement of the method is also that the vacuum treatment must not result in damage to the structure of the bakery product, in particular the surface or crust thereof. This represents a serious problem which for the first time has been solved with the present invention insofar as large capacity cooling is concerned.